1 Department of Occupational Lung Disease, Royal Brompton and Harefield NHS Foundation Trust, London SW3 6LR, UK. Electronic address: j.feary@Imperial.ac.uk.
2 Department of Occupational Lung Disease, Royal Brompton and Harefield NHS Foundation Trust, London SW3 6LR, UK.
3 Brighton and Sussex Medical School, University of Sussex, Falmer, Brighton, UK.
4 Department of Occupational and Environmental Medicine, Imperial College, London, UK.